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V3 Supercharger vs. New Tesla Plug vs. Double Tesla Plugs

Discussion in 'Design' started by Tom Bodera, Mar 1, 2017.

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  1. Tom Bodera

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    I was just thinking about the tweet from Elon about the possible new Supercharger going past 350kw. I was thinking about how this much higher amperage/voltage would affect the current Tesla connector and how it might have to change. The current connector is rated for ???. However looking at the sizes of these plugs (combo/CCS and Chademo) note the possible wire guage differences. It would be nice to keep the plug the same but if we are to double the current would Tesla move to double connectors(keeping the old one but two of them) or update to a new connector. I do not see how they could increase the guage of the connector and maintain the plug shape/socket. Thoughts?

    [​IMG]
     
  2. TrevP

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    They tried liquid-cooled cables...

    I don't think they're going to be changing the North American Tesla plug standard for 350Kw anytime soon. Im thinking at this point Model 3 was designed to handle any new higher power standards given the design timeframe of the car and the new battery pack systems. Model S and X will eventually have the new cells/pack in time. Europe imposes the type 2 connector on Tesla so anything can change over there.

    Lastly, these large plugs (anything over the type 2) just don't fit in the Tesla taillight housing so where would they put the connector? Their design aesthetic pretty much dictates they will stay within current plug confines.
     
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    • Twiglett

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      Don't European (or all non-US) Tesla all use the Mennekes type 2 connector?
      I seem to remember that the European chargers (not Tesla) need you to have your own cable as well.
       
    • Bobby Garrity

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      This is actually something that I have been wondering about quite a bit. What is the theoretical power limit of the Tesla connectors (or any of the other connectors for that matter)? We know that 120kW is the Supercharger limit for V2, but not necessarily the connector. Does the connector even have a power limit? That is, is it the physical connector that matters or other parts of the specification? Do the amount of pins matter?

      I would love to have someone who is an expert on the subject comment on these things.
       
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      • Badback

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        The connector has a CURRENT limit. As current passes through a connector, some power(heat) is lost at the contact point. The connector has some small resistance. The heat (power) loss is equal to current^2*resistance (I^2R). The contacts heat up as current increases. Some of this heat is conducted to the body of the connector, which will eventually melt, long before the metals in the contacts melt. Usually resistance will increase with temperature which will result in a run away temperature rise.

        So, the current limit is that which will compromise the safe use of the connector.
         
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        • Bobby Garrity

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          Ah. So that explains why I keep hearing about the high voltage of DC fast charging but not high current.

          Tesla offers two current options for the charger, 48A and 72A with the High Amperage Option, which affects how fast you charge on the Wall Connector. Would you happen to know if that higher current could possibly lead to faster on Supercharging as well (if, of course, Tesla chose to implement that), or if there is another technical reason why they cannot go beyond the current current limit?
           
        • Badback

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          Superchargers are DC systems. The current does not go through the on-board charger. The on-board charger contains a rectifier circuit to change the AC supply from level 1 or 2 sources to DC. These rectifiers have a maximum current rating which must not be exceeded.

          A few words about the voltage boosting circuits: In order to push current into a 400V battery, the charger has to output greater than 400V.
          This is done by a voltage boost circuit. I do not know the particulars of how Tesla is doing this. The Wikipedia article offers a basic explanation: https://en.wikipedia.org/wiki/Boost_converter
           
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          • arnis

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            It appears Tesla US plug is running near max current it can handle in ideal conditions, 335A.
            Same is for non-US solution, aka enhanced Type2.
            Actually often 335A is not available. And some of those instances it appears to be the coupling limitation.

            When Elon mentioned 350kW, he mentioned charger, not the stall. That's a big difference.

            I'm betting that Model 3 will have "enhanced Combo2" style port, that supports Type2 enhanced SC plug
            and also CCS-s that will be soon available. It's bigger than S/X but M3 taillight design appear to have bigger flap too.

            I can't imagine what happens in US. Maybe M3 will keep the regular port on drivers taillight and add "not enhanced Combo1" to other side.
            In near future CCS will be more available than ChaDeMo today. Everywhere, except Asia I believe.
             
          • John

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            Seems like the best answer is a much higher charge voltage, to reduce the current that needs to flow through the connector for any given power level. After the connector (inside the car), you can step the voltage back down (and the current up) at the point it interfaces the battery. For instance, a 120 kW charger at 400 V nominally transfers a bit more than 300 A. A 1200 V system could transfer that same power using just 100A. Or more likely for the original 300 A it could provide over 350 kW.

            I also think another key to fast charging is to have a flexible cell switching architecture that lets you charge in one configuration (more of the cells in parallel, charging all at once with independent current paths) and then the car runs in another configuration (more of the cells in parallel). This is in keeping with Tesla's design philosophy, which can be summed up as "electronics and software are cheap." (To wit: this is why they use AC induction motors rather than DC motors).
             
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            • Tom Bodera

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              Problem with Higher voltage would be that the arc length between the contacts is higher. This may be a problem with the distance between the two connectors on the current plug (400v vs. 1200v).

              Anybody have any technical idea if two separate existing tesla connectors could be used in parallel for increased power transfer?
               
            • arnis

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              Absolutely yes.
               
            • John

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              #12 John, Mar 6, 2017
              Last edited: Mar 6, 2017
              The charger is much smarter than this, and that the voltage isn't even applied until after handshaking occurs with the car. So arcing isn't an issue.

              That having been said, just to sort the physics out, the spark gap increases from 0.001 inch (0.03 mm) to 0.006 inch (0.15 mm) when you go from 400 V to 1200 V.
              You can check it here:
              http://www.cirris.com/learning-center/calculators/50-high-voltage-arc-gap-calculator

              So according to this measure, the contacts are much farther apart than this, and won't arc from one to another even if the cable was live prior to plugging in. (Remember, a spark plug requires something like 20,000 volts to jump a millimeter or two, and the bare metal on the plug are probably 10x this far away, separated by insulating plastic walls.)
               
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              • arnis

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                #13 arnis, Mar 6, 2017
                Last edited: Mar 6, 2017
                Unfortunately electricity is not that simple. Arch is more complicated than that.
                Especially DC arch. It is not self-extinguishing like AC arch.
                Numbers you gave are for dielectric medium. But arch itself is excellent conductor.
                Engineering is more complex and 1200V is definitely NOGO for Tesla SC connector.
                Coupling will not be able to exctiquish 1200V DC arch if locking mechanism fails.
                And this is the main presumption - locking mechanism can never be trusted 100%.
                I've seen multiple ChaDeMo chargers that have connectors heavily burned.

                Ok', I'll stop talking and just demonstrate, what is the difference between
                220V AC and 220V DC arch under load.
                 
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                • Tom Bodera

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                  Wow. Great info and presentation.
                   
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                  • arnis

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                    Thank you. I'm having a hard time at M3OC proving that I'm not an idiot.
                     
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                    • John

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                      #16 John, Mar 6, 2017
                      Last edited: Mar 6, 2017
                      Don't Teslas include arc detection in their control circuitry?
                       
                    • arnis

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                      #17 arnis, Mar 6, 2017
                      Last edited: Mar 6, 2017
                      The fact that arc exists means something is wrong with management electronics (for example damage occurred and control compromised). Any non-isolated detection mechanism is not reliable in this scenario.
                      Usually loss of pilot/control signal would stop the current. How many milliseconds SuperCharger needs to stop the flow after pilot signal is not in range is most likely only known by few Tesla engineers.
                      But having SC disconnected doesn't mean the end. If arcing is already happening it might also happen on car side as well.
                      I don't have information is the "onboard charger bypass contactor" capable to disconnect 100-1000A current. Most likely not. It would be gigantic in size. The fuse in the pack might not blow (designed for drivetrain protection, not supercharging, 1300A or 1500A depending on pack version).

                      That relay most likely separates contacts in normal atmosphere with only few millimeter distance with nothing for arc suppression.
                      Detecting DC arc is not enough. Disconnecting load will not work and opening regular relay will only make new arc in the relay.
                      If Tesla has another fuse on the DC input line, then this will solve everything. Would be awesome to know the value.

                      Thinking exercise:
                      Imagine 1200V Tesla. You have an accident at supercharger. Somebody drove into the stall and ripped the plug out of your car.
                      Supercharger de-energizes in fraction of a second. But arc is already stable at the vehicle port side. How would you extinguish the
                      arc if it draws below 1500Amps. And there are no additional fuses besides the one in the pack rated for 1500A made out of inconel.
                      Video above visually shows how long the arc will be in open air if was initiated at 220V 12A.
                       
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                      • John

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                        Relays? Don't they use high voltage IGBTs such as the ones JB has discussed from time to time on both sides of the connection? IGBTs can handle well over 4KV at 90A, in parallel if necessary to meet current requirements.

                        The essence of a control circuit is that it isolates the circuit when disabled or shorted. Just like you can't shock yourself by cramming snow or fingers inside the charging port of your Tesla, you can't sustain an arc after the plug is removed.
                         
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                        • arnis

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                          There are no semiconductors between li-ion cells and supercharger inverters (a dozen in each box) when DC-charging.
                          [​IMG]

                          If you stop the current flow before arc jumps into direct contact between positive and negative sides there will be only a slight carbon residue at the place where two conductors were separated.

                          IGBTs are used in powertrain inverters. They can't be used as fuses. They need to be fused as one of their failure modes is short circuiting.
                           
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                          • John

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                            My main point is that if you've got arcing at the connector, you've got a system failure— whether you used a relay or a solid state component, or 400 V or 1200 V. As you've shown, arcing has to be prevented either way. And from an overall heat, cost, and efficiency perspective, high voltage would help. You just need efficient voltage conversion and fast protection circuitry.
                             
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